1. Field of the Invention
The present invention relates generally to automatic transmission system for heavy construction equipment and more particularly to automatic transmission systems in which an ECU (Electronic Control Unit) calculates change of the running speed to automatically shift gears under optimal conditions.
2. Description of the Prior Art
Semi-automatic transmission systems have generally been used for conventional heavy construction equipment. Such semi-automatic transmission systems, however, cause much inconvenience to the driver due to manually shifting gears in accordance with acceleration and deceleration of the vehicle.
Furthermore, heavy construction equipment commonly employs a two-speed transmission system having a first-speed (low-speed) gear and a second-speed (high-speed) gear. The ratio of the first-speed gear to the second-speed gear is about 6.876:1.80 and a ratio of the maximum running speeds thereof is about 9 Km/h:33.4 Km/h. Therefore, when shifting the gears, ill effects such as shocks may be caused.
In order to prevent the shocks when shifting gears and in particular, an overturn of the vehicle-body due to an abrupt speed reduction according to the gear ratio when shifting from high speed to low speed, and to save the expected life span of the transmission system, a governor should be employed which disallows the gear-shifting unless the running speed at a moment when down-shifting the gears from second-speed to first-speed reaches the maximum running speed range (9Km/h) of the first-speed gear. However, the employment of such a governor leads to very complicated hydraulic circuits.
Referring to FIG. 1, a conventional transmission system for heavy construction equipment must include a first-speed clutch 101 for engaging a first-speed gear, a second-speed dutch 102 for engaging a second-speed gear a control valve 103 for selectively supplying pressurized oil to the first-speed clutch 101 or the second-speed clutch 102 to shift the gears, a governor valve 104 and a reset valve 105 for preventing shocks upon shifting the gears.
The present invention is made to achieve a solution to the above-mentioned problems concerning the operation of the transmission and the complicated make-up of the flow circuit, the inventor underwent extensive research which resulted in the present invention.